Noise reduction apparatus and method

ABSTRACT

An apparatus and method for operating an auxiliary hydraulic load at low noise levels. A pump having a capacity which is sufficiently large to supply the load with the necessary volume of hydraulic fluid at relatively low pump speeds is driven by an engine operating at a speed near its idling speed. Throttle control means control the fuel supply to the engine at a level sufficient to drive the pump while maintaining the engine speed near its idling speed. When the engine speed is increased to a predetermined level in excess of its idling speed, means are provided to maintain the output from the pump at or below a predetermined flow rate to not overload the pump means or the auxiliary load. The pump may include a variable displacement pump or a plurality of fixed displacement pumps with means to vary the pump output in response to the pressure demand from the auxiliary load to maintain the torque input requirements for the pump below a predetermined level. The throttle control means may be actuated in response to the pressure demands of the auxiliary load to vary the torque from the engine in response to the torque input required for operation of the pump while the engine is operating at a speed near its idling speed.

This is a division of application Ser. No. 274,798, filed July 24, 1972,now abandoned.

BACKGROUND OF THE INVENTION

With the increasing concern of society in protecting and improving theenvironment, the problem of noise pollution is receiving much study.People who live in cities are surrounded by all manner and variety ofnoises ranging from the roar of jet planes to the rumble of freewaytraffic. This vast accumulation of noise can be quite harmful in causingdiminished hearing. Also, although not precisely measurable, noise canand does have an adverse effect upon the emotional stability and mentalhealth of the recipients.

People are now asking seriously whether machines created to be servantsof man are not, in fact, becoming his master. Surely, this is a fairquestion in regard to noise pollution where the constant cacophony ofmachine noises disrupts man's thinking processes, interferes with hissleep, and oftentimes threatens to destroy his sanity.

A common source of noise in the city is the strident noise of a truckengine as it turns over at high speeds in operating the auxiliaryequipment carried on the truck. As one example, consider the noise of atruck engine in operating the packing mechanism for refuse collectionequipment during the pick up of refuse in a residential neighborhood.The collection of refuse begins early in the morning and, thus, thenoise of the laboring truck engine operating at high speed may well bethe first sound which greets the ear of a city resident on awakening.Even worse, the noise of the truck engine may be the causation for anunwanted early awakening by the sleeper.

Many types of auxiliary truck equipment, such as the packing mechanismfor a refuse loader, go through a cycling operation in which the loadrequirements on the engine will vary. Thus, for example, in theoperation of a refuse packing mechanism, the refuse will first be placedin a hoper positioned within a tailgate structure on a truck. The refuseis then swept from the hopper and moved through an opening connectingthe hopper with a refuse storage body positioned on the truck frame. Asthe refuse is moved into the opening and packed under great pressures,the pressure demands of the packing mechanism are very high. Thepressure demands at this stage of packing are generally considerablyhigher, for example, than the pressure demands when the refuse is beingswept from the hopper. For a more detailed description of a refusepacking mechanism, reference is made to U.S. Pat. No. 2,879,906, issuedMar. 31, 1959.

During operation of an auxiliary load on a truck, it has previously beennecessary to maintain the truck engine at a relatively high speed whenthe auxiliary load is variable, as in the case of a refuse packingmechanism. This was done to prevent the truck engine from stalling whenthe power demands imposed by the variable load were increased. Toprevent stalling, it was customary to maintain the truck engine at arelatively high speed to provide the output from the engine at a levelsufficient to operate the variable load under the maximum powerconditions imposed by the load. This method of operation, while perhapssatisfactory to prevent stalling, was inefficient and produced a highnoise level from the truck engine in driving the auxiliary load.

By maintaining the engine speed at a level to supply the maximum powerdemand from the auxiliary load, the engine produced more power than wasneeded by the load at power demands less than its maximum. To dissipatethis unused power during the minimum power demand portions of thevariable load cycle, it was necessary to shunt a portion of the outputfrom a pump driven by the engine to a sump during the minimum powerdemand portions of the variable load cycle. Thus, the full output of thepump was used only during the maximum power demand portions of thevariable load cycle.

In the operation of auxiliary equipment, some manufacturers have mountedan auxiliary engine on the truck to operate the auxiliary equipment. Theauxiliary engines are relatively small and operate at a high rate ofspeed to develop their maximum horse-power in driving the auxiliaryequipment. This type of operation has not been satisfactory in terms ofabating noise pollution since a small engine operating at a high speedis a very efficient generator of noise. Also, this type of operation isinefficient since it requires dissipation of unusable engine outputexcept when the load is in the maximum power demand portion of itscycle.

SUMMARY OF THE INVENTION

In providing a solution to the above problems, the present inventionprovides an apparatus for operating an auxiliary mechanism at greatlyreduced noise levels. In addition, the present invention provides anapparatus and a method for driving a variable auxiliary load in whichthe driving power is more efficiently utilized by the load. Also, itprovides an apparatus and a method in which an engine that drives anauxiliary load is operated at a relatively low speed near the engineidling speed. This results in reduced engine wear, increased engine lifeand reduced maintenance costs as compared with previous devices in whichan engine providing power for a variable auxiliary load was operated ata relatively high rate of speed to prevent engine stalling.

In accord with the invention, a variable volume or variable pressureauxiliary hydraulic load is driven by a pump means having a capacitysufficiently large to supply the demands of the load when the pump meansis operating at relatively low speeds, which may be 1,000 rpm. or less.Engine means are operably connected to the pump means for supplyingpower to the pump means. The operation of the engine in supplying powerto the variable auxiliary hydraulic load is at a relatively low speednear the idling speed of the engine. With a truck engine, which operatesat a relatively high speed, such as about 4000 rpm., in powering a truckover the highways, the engine operates at a relatively low speed nearits idling speed in powering the auxiliary load which may be about 700to about 1,000 rpm. or less. When operating in this manner, the enginemeans is operating at about one-quarter or one-third or less of itsmaximum speed and horsepower and, thus, operates at a low noise level inproviding power for operation of the auxiliary load.

During operation of the auxiliary load by the engine means, throttlemeans may control the fuel supply to the engine at a level sufficient tomaintain its horsepower output at a level to operate the pump meanswhile also maintaining the speed of the engine means at about its idlingspeed or slightly higher. When the engine speed is increased to apredetermined level, for example, in performing its primary workfunction, means are provided to maintain the flow rate of fluid throughthe pump means at or below a predetermined level based on its capacity.Thus, if the engine means were providing power to the auxiliary load atan engine speed of 700 rpm. and the engine speed was then increased toconcurrently power a truck while driving the auxiliary load, the flowrate through the pump would be maintained at a level that does notexceed the capacity of the pump. In one form of the invention, this isaccomplished by providing a centrifugal clutch in the drive trainbetween the engine means and the pump means. Thus, when the engine speedexceeds a predetermined level, the clutch automatically disengages thedrive between the engine means and the pump means.

In the use of the apparatus of the present invention for operation of avariable volume and variable pressure auxiliary hydraulic load, a fluidreservoir may be provided in flow communication with the pump means toprovide an open loop hydraulic circuit which includes the pump means andthe variable load. This provides greater flexibility in the functioningof the apparatus by providing a variable volume of hydraulic fluid foroperation of the auxiliary load. For example, if the variable loadincludes a hydraulic cylinder having a relatively large volume, a largevolume of hydraulic fluid will be stored within the cylinder during aportion of its operation. The reservoir provides a source of hydraulicfluid to supply the cylinder and the stored hydraulic fluid can then bequickly discharged to the fluid reservoir during another phase of theload cycle when the load does not require a large volume of fluid.

The pump means employed to operate the auxiliary may be a fixeddisplacement pump whose capacity is sufficiently large to satisfy themaximum volume of hydraulic fluid demanded by the variable load. Thepump means is driven by an engine means whose torque output, whenoperating at a speed near its idling speed, is adequate to supply thetorque input required to operate the pump means in powering theauxiliary hydraulic load. the

In another embodiment of the invention, the pump means may include avariable displacement pump and means for reducing the displacement ofthe pump in response to increased pressure demands from the variableload. The input torque required to drive the pump means is proportionalto the volume of fluid being pumped by the pump means and also to thepressure demands of the variable hydraulic load. Thus, when the pressuredemands of the variable hydraulic load rise to a predetermined level,the displacement of the variable displacement pump may be reducedproportionately to maintain the input torque required to drive the pumpmeans at or below a predetermined level. In this manner, the enginemeans is able to supply the necessary power required to drive the pumpmeans while operating at a relatively low speed near its idling speed.

In another embodiment of the invention, the pump means may include aplurality of fixed displacement pumps with means for varying the numberof pumps in operation in response to the pressure demands of thevariable hydraulic load. By reducing the number of fixed displacementpumps in operation when the pressure demands of the variable hydraulicload reach a predetermined level, the torque required to drive the pumpmeans may be maintained at or below a predetermined level. Then, whenthe pressure demands of the variable hydraulic load are reduced, thenumber of fixed displacement pumps in operation may be increased toincrease the volume of hydraulic fluid and to increase the speed ofoperation of the variable load while maintaining the torque inputrequirements of the pump means below a predetermined level.

In a further embodiment of the invention, a throttle control means mayvary the fuel supplied to the engine means in response to the pressuredemands of the variable load. The torque output produced by the enginemeans may then be varied in response to the pressure demands of thevariable load while the volume of the fluid discharged to the system bythe pump means is likewise varied in response to the pressure demands ofthe variable load. The torque output of the engine means may, thus, becontrolled so that it matches the input torque required for operation ofthe pump means. This provides a more efficient operation in which thetorque output of the engine is more effectively utilized by the pumpmeans in driving the auxiliary load.

In a further embodiment of the invention, a throttle control device maybe employed which varies the fuel supplied to the engine in response toboth the pressure demands of the auxiliary load and the volume ofhydraulic fluid supplied to the load by the pump means. When used with apump means which includes a plurality of fixed displacement pumps, thethrottle control device may receive a pressure input which isproportional to the system pressure and the load demands of the variableauxiliary load and a pressure input which is proportional to the volumeof hydraulic fluid supplied to the system by a pump which dischargesfluid to the system when the system pressure is at or below apredetermined pressure. The combined pressure inputs to the throttlecontrol device, based on both the system pressure and the volume offluid discharged to the system by the pump means control the movementimparted to a throttle control lever by the throttle control device. Thequantity of fuel supplied to the engine and the output torque of theengine are, thereby, controlled by both the volume of fluid dischargedto the system by the pump means and the system pressure against whichthe pump means works in supplying the variable hydraulic load withfluid.

Through use of the present apparatus and method, a relatively largeengine is used to provide the power for a relatively small auxiliaryload. In providing the power for the auxiliary load, the engine isoperated at a relatively low speed near its idling speed. When operatedin this manner, the engine means may be operating at about 25 percent orless to about 34 percent of its maximum speed and horsepower. The enginemeans thereby provides the power for the auxiliary load at a very lownoise level. The output torque generated by the engine means and theinput torque required by the pump means in supplying the auxiliary load,are preferably interrelated so that overall efficiency is maximized withthe output torque from the engine means being effectively used indriving the pump means.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are to be regarded as merely illustrative of theinvention:

FIG. 1 is a schematic view of a system in which an engine operating nearits idling speed provides the power at a low noise level to perform asecondary work function in operating an auxiliary load;

FIG. 2 is a schematic view of a variable displacement pump which may beused in the system illustrated in FIG. 1;

FIG. 3 is a schematic view of a pump and valve arrangement which may beused in the system of FIG. 1 to provide a plurality of fixeddisplacement pumps to drive the auxiliary load with the number of pumpsin operation being varied in response to the pressure demands of theauxiliary load;

FIG. 4 is a schematic view of the pumps and valving engagementillustrated in FIG. 3 in which the valve has been shifted to decreasethe volume of fluid discharged to the system in providing power foroperation of the auxiliary load;

FIG. 5 is a side sectional view of a throttle control device which maybe used to vary the fuel supply to the engine in response to thepressure demands of the auxiliary load and the volume of fluiddischarged to the system by the pump, and

FIG. 6 is a side elevational view of a refuse collection vehicle showingin phantom line drawing a packing mechanism operated by a pump driven bythe vehicle engine at a speed near its idling speed.

DETAILED DESCRIPTION

With reference to FIG. 1, a relatively large engine 2 whose primary workfunction may be in driving a truck through a main output shaft 7, isutilized to perform a secondary work function in providing power tooperate an auxiliary load 4 through an auxiliary output shaft 8. Theauxiliary shaft 8 is connected through a centrifugal clutch 26 to aninput shaft 9 to a pump 6. The pump 6 receives hydraulic fluid throughan input line 16 from a reservoir 14 and delivers hydraulic fluidthrough an output line 10 to the variable volume and variable pressureauxiliary load 4. Hydraulic fluid from the auxiliary load 4 is returnedto the reservoir 14 through a return line 12.

A control line 28 may be provided which leads from the output line 10 tothe pump 6 with the control line being used to vary the volume ofhydraulic fluid delivered by pump 6 through the output line 10. However,it is not essential that the volume of hydraulic fluid delivered by thepump be varied. Thus, the control line 28 may be regarded as structurewhich is optional. The pump 6, for example, may be a fixed displacementpump whose capacity is sufficiently large to satisfy any demand placedon it by the variable auxiliary load 4. The engine 2 is then sized sothat it provides the necessary power to operate the pump 6 with theengine 2 operating near its idling speed.

A control line 18 leading from the output line 10 may be utilized tooperate a throttle control device 20 which is depicted as a hydrauliccylinder. A rod 22 which is movable in response to pressure changeswithin the throttle control device 20 is connected to a throttle 27through a throttle lever 24. As the pressure demands of the auxiliaryload 4 are increased, additional power is required to drive the pump 6to provide hydraulic fluid for the load 4. The increased power demandsof the load 4 are met by incresing the fuel supplied to the engine 2with the quantity of fuel being dependent upon the system pressure inline 10, as transmitted through control line 18 to the throttle controldevice 20. Thus, the torque output from the engine 2 may beautomatically regulated by the throttle control device 20 to provide thenecessary power for operation of the auxiliary load 4 while maintainingthe speed of the engine 2 near its idling speed.

In providing the power for operation of the auxiliary load 4, the engine2 operates at a speed near its idling speed. Thus, where the primarywork function of the engine is to provide power for operation of atruck, the engine may operate at a speed which is about one-quarter orless to about one-third of its maximum speed in providing a horsepoweroutput to the auxiliary load of about one-quarter or less to aboutone-third of its maximum horsepower output. For example, the speed ofthe engine 2 may vary from about 700 or less to about 1,000 rpm. inproviding the power for operation of the auxiliary load 4.

Due to its operation near its idling speed in supplying power to theauxiliary load 4, the engine 2 provides the necessary power at very lownoise levels. Moreover, by operating the engine 2 at a relatively lowspeed in providing power for the auxiliary load 4, the life of theengine is extended and maintenance costs are reduced. In operating theauxiliary load 4, stalling of the engine 2 may be prevented by varyingthe fuel supplied to the engine 2 in response to the pressure demands ofthe variable load 4. The output from the engine is, thus, varied to meetthe demands of the load so that the engine output is efficiently used bythe load.

The maximum speed and horsepower of the engine 2 are far in excess ofthat required for operation of the auxiliary load 4. If the speed of theengine 2 was increased to its maximum speed, this would drive the pump 6at speeds in excess of its capacity and also would result in supplying aquantity of fluid to the load 4 which exceeded its capacity. Thecentrifugal clutch 26 is used to protect the pump 6 and load 4 frombeing overdriven by the engine 2. When the engine speed is increased toa predetermined speed in excess of its idling speed, as, for example,when the engine is performing its primary work function, the clutch 26automatically disengages the auxiliary output shaft 8 from the inputshaft 9. For example, the clutch 26 may be set to disengage to shaft 9when the speed of the engine 2 is increased to about 1,500 rpm.

As illustrated, the auxiliary output shaft 8 is directly driven by theengine 2 so that the shaft rotates continuously when the engine isoperating. The apparatus is controlled through actuation of the clutch26. Various means may be used to control the clutch and one means, forexample, may consist of a simple electrical circuit in which a pluralityof switches 15, 17, 19 and 21 are connected in series by an inputconductor 11 between a source of electrical power 23 and the clutch 26.The switch 21 may be actuated by the ignition system of a vehicle whichis powered by the engine 2 such that switch 21 is closed by turning theignition key in starting the engine.

The switch 19 may be positioned on the dash within a vehicle cab whilethe switch 17 may be positioned anywhere on the vehicle which isconvenient to the load 4. In a refuse packer where the packing mechanismis positioned on the rear of the truck body, the switch 17 wouldgenerally be positioned at the rear of the truck body for ease inoperating the packing mechanism. The switch 19 serves as a safetymeasure to prevent injury of children or trespassers through actuationof the switch 17. With switch 19 in an open position, the apparatuscannot be operated out of the view of the driver by the closing ofswitch 17.

The switch 15 is a speed control switch which may be connected to theengine through a conductor 25. The conductor 25 transmits a signal toswitch 15 when the engine 2 reaches a predetermined speed. When theengine 2 exceeds the predetermined speed, the switch 15 is automaticallyopened to open the clutch 26 and disengage the connection between shafts8 and 9. This prevents overdriving of the pump 6 or load 4 by the engine2. As illustrated, the electrically operated clutch 26 may be groundedin a conventional manner through a conductor 13.

The switch 15 may be actuated mechanically as well as electrically. Forexample, the switch 15 may be opened and closed in response to the speedof rotation of a drive cable connecting the switch 15 to the engine 2.The drive cable which would serve the same function as the conductor 25,may be driven from the shaft 8 in the manner of a speedometer cable.Also, the switch 15 may be made integral with the clutch 26 and beactuated by centrifugal force.

The signal transmitted to the switch 15 through conductor 25 may begenerated by sensing the speed at which the distributor contacts areopened and closed or by directly sensing the speed of rotation of shaft8. For example, a small generator may be driven from a power takeoff togenerate an electrical output whose magnitude is directly proportionalto the speed of the engine 2. To provide system flexibility, the switch15 may be adjustable. Then, the switch 15 may be set to open at anydesired engine speed as required to protect the particular pump and loadpresent in the system.

A reservoir 14 interconnects the variable load 4 and the pump 6 toprovide flexibility in the system so that a variable volume of hydraulicfluid may be used in operating the load 4. If, for example, the loadincludes hydraulic cylinders having a relatively large volume as used inpowering the packing mechanism for a refuse loader, the cylinders maystore relatively large quantities of fluid during certain phases of theload cycle. As this occurs, relatively large quantities of hydraulicfluid are withdrawn from the reservoir 14 and transferred to the load 4through the pump 6. At another point in its operation, the variable load4 may require a relatively small quantity of fluid for operation. Arelatively large quantity of hydraulic fluid would then be stored in thereservoir 14 with a small quantity of hydraulic fluid being used tooperate the load 4.

FIG. 2 illustrates a conventional variable displacement pump 29 whichmay be used in the overall system illustrated in FIG. 1. The variabledisplacement pump 29 includes a swash plate 30 on a pivotal mounting 36which engages a pair of pistons 40. The pistons are contained in boreswithin a pump body 38 and are biased outwardly by springs 42 intocontact with the swash plate 30. Retainer rings 44 fixedly positioned onthe pistons 40 adjacent their outward ends contact the outer portions ofthe springs 42 while the inner portions of the springs bear against thepump body 38. The pump body 38 may be rotated by an input shaft 9 withthe stroke of the pistons 40 being determined by the angle of the swashplate 30.

A control rod 32 is connected to swash plate 30 through a pivotalconnection 33 and is movably positioned by a hydraulic cylinder 34 whichreceives fluid through control line 28. A piston 37 slidably positionedwithin the cylinder 34 is connected to the control rod 32 while a spring35 positioned between the end of the piston 37 and the inner wall ofcylinder 34 exerts an outward force on the piston 37 and control rod 32.The outward force exerted by the spring 35 serves to position the swashplate 30 at an angle to provide the maximum displacement of the pistons40.

When the pressure in control line 28 is increased, which reflects anincreased system pressure and an increased pressure demand by the load4, the piston 37 and control rod 32 are moved to the left from theirpositions as shown in FIG. 2. This causes a counterclockwise rotation ofthe swash plate 30 toward a vertical position and thereby reduces thedisplacement of the pistons 40. This, in turn, reduces the dischargefrom the variable displacement pump 29. The torque required to drive thevariable displacement pump 29 is dependent upon the system pressure inline 10 and also on the volume of fluid being discharged to the systemby pump 29. By reducing the volume of fluid discharged from the pump 29in response to an increase in the pressure demand of the load 4, thetorque input required to drive the pump 29 is maintained below apredetermined level. This provides greater system flexibility because itpermits the pump 29 to be driven with a relatively low output torque andoutput speed of the engine 2 without stalling the engine even throughthe pressure demands of the auxiliary load 4 may have increased sharply.

Turning to FIG. 3, there is illlustrated a schematic diagram of aplurality of fixed displacement pumps which ar operated by a valvingsystem to vary the discharge from the pump 6 to the system in responseto the pressure demands of the auxiliary load 4. As illustrated, a pairof fixed displacement pumps 46 and 48 are driven from a common inputshaft 92 which corresponds to the shaft 9 illustrated in FIG. 1. Thedischarge from the pumps 46 and 48 is controlled by a valve 50 whoseposition is varied in response to the pressure demands of the auxiliaryload 4. An inlet line 52, which is indicated as split into two lines 56and 58, feeds fluid to a common suction for each of the pumps 46 and 48.

The discharge from pump 46 and the discharge from pump 48 are fedthrough outlet lines 60 and 62, respectively, to the valve 50. With thevalve 50 positioned as shown in FIG. 3, the outlet 60 from pump 46 leadsto a valve cavity 64 and to a valve passage 66. The discharge from pump46 then flows through the valve passage 66 to a valve cavity 68 and to adischarge line 70.

The outlet line 62 from pump 48 leads to a valve cavity 72, then to avalve passage 74, and to a valve cavity 76. The discharge from the pump48 is, thus, fed to the valve cavity 76 and then to a discharge line 78which joins the common discharge line 70. With the valve 50 in theposition illustrated in FIG. 3, the discharge from both pumps 46 and 48is, thereby, fed through the valve 50 to the common discharge line 70.

A pressure control line 90 may be connected to the common discharge line70 to indicate the system pressure which is determined by the pressuredemands of the variable load 4. A second pressure control line 88 may beconnected to the valve cavity 64 to sense the pressure of the dischargefrom the pump 46 when this discharge is fed to the system. The pressurecontrol lines 88 and 90 may then be used to operate a throttle controldevice as shown in FIG. 5 which varies the rate of supplying fuel to theengine to vary its torque output in response to the pressure demands ofthe system and the volume of fluid discharged to the system by the pumps46 and 48. It is not necessary, however, that two pressure control linesbe used to operate the throttle control device and, if desired, thethrottle could be controlled entirely by system pressure as transmittedthrough control line 90.

A control line 80 is connected to the discharge line 78 and senses thedischarge pressure generated by the pump 48. The line 80 leads to apressure opening valve 82 which is adjustable to open at a predeterminedpressure. Leading from the valve 82 is a control line 84 connected to anactuating device, illustrated as a hydraulic cylinder 96, which isoperably connected to the valve 50. The hydraulic cylinder 96 worksagainst a spring 94 which is illustrated in FIG. 3 as pushing the valve50 to the right with the spring in an expanded condition.

A valve cavity 86 overlies a return line 54 leading from the valve 50 tothe input line 52. When the valve 50 is in the position shown in FIG. 3,the return line 54 is covered by the valve cavity 86 and does nottransmit hydraulic fluid.

As the speed of the engine and the rotational speed of the input shaft92 are increased during operation of pumps 46 and 48 in working againsta variable hydraulic load, the pressure in line 80 gradually builds upto the predetermined opening pressure for valve 82. When the pressure inline 80 is sufficient to open valve 82, the pressure is then transmittedthrough line 84 to the hydraulic cylinder 96. This causes the valve 50to shift to the left from its position as shown in FIG. 3, with excessfluid in addition to that required to operate cylinder 96 being fed fromcylinder 96 through a bleeder or return line 100 to a sump 98.

The valve 50 is shown in its shifted position in FIG. 4, after havingshifted in the direction of the arrow A. With the valve shifted, theoutlet line 60 from pump 46 leads to the valve cavity 86 and then to tereturn line 54. The discharge from the pump 46 is, thus, recycledthrough line 54 to the inlet line 52 and is returned through lines 56and 58 to the common suction for pumps 46 and 48. After shifting of thevalve 50, the discharge line 62 from pump 48 is still connected throughthe elongated valve cavities 72 and 76 to the discharge line 78. Thus,after shifting of valve 50 in the direction of arrow A, only thedischarge from pump 48 is conveyed through the valve to the dischargeline 70.

When the valve 50 has shifted to its FIG. 4 position, there is areduction in the flow rate of hydraulic fluid into the system since thedischarge from pump 46 is recycled. The input torque required to drivepumps 46 and 48 through input shaft 92 is proportional to the volume offluid discharged by the pumps 46 and 48 to the system and also to thesystem pressure in line 70. Thus, the reduction in flow rate caused bythe shift of valve 50 causes a sharp reduction in the input torquerequired to drive pumps 46 and 48.

When the valve 50 is in its shifted position, the pressure in valvecavity 64 drops to zero. This causes a corresponding reduction in thepressure in control line 88. Due to the drop in pressure in control line88, the only pressure received by a throttle control device is throughcontrol line 90. The overall pressure received by a throttle controldevice is thus sharply reduced which may be used to cause acorresponding reduction in the quantity of fuel being fed to the engineand the output torque generated by the engine to match the decreasedinput torque then required for operation of pumps 46 and 48.

When the pressure in control line 80 drops below the predeterminedopening pressure for valve 82, the valve closes and the spring 94expands to return valve 50 to its position as shown in FIG. 3. As thisoccurs, hydraulic fluid in the hydraulic cylinder 96 is exhaustedthrough a line 100 to a sump 98. With the valve 50 returned to its FIG.3 position, the discharge from both pumps 46 and 48 is again fed to thecommon discharge line 70 to supply an increased volume of hydraulicfluid to the variable load 4. Also, with the valve 50 in its returnposition, the pressure sensed by control line 88 is the dischargepressure from the pump 46. This pressure may be transmitted throughcontrol line 88 to a throttle control device together with the systempressure through control line 90. This increased pressure may be used tocause an increase in the quantity of fuel being fed to the engine toprovide a greater output torque to match the increased input torque thenrequired when both pumps 46 and 48 are discharging hydraulic fluid tothe load system.

The combination of pumps and valving illustrated in FIGS. 3 and 4 iscommercially available equipment. It may, for example, be purchased fromTyrone Hydraulics, Inc. of Corinth, Mississippi as part numbersSH20250-200A-DJ or SH20-300-250A-DJ. If a volume responsive or a volumeand pressure responsive valve is used in the system of FIGS. 3 and 4 inlieu of the pressure responsive valve 82, the system may be maderesponsive to the volume of fluid discharged by pumps 46 and 48 or toboth the volume of discharged fluid and also the system pressure inregulating the volume of fluid discharged to the load system by pumps 46and 48.

FIG. 5 illustrates a throttle control device 102 which is particularlysuitable for use in the system described in FIGS. 3 and 4. The throttledevice 102 includes a body 104 having an enlarged central body cavity106 and a reduced central body cavity 108. A piston 110 is positionedwithin the enlarged and reduced body cavities 106 and 108 and has anenlarged diameter portion 112 received by cavity 106 and a reduceddiameter portion 114 received by cavity 108. A sloped transition wall117 interconnects the diameters of the enlarged cavity 106 and thereduced cavity 108. With the piston 110 in retracted position as shownin FIG. 5, the enlarged diameter portion 112 bears against the juncturebetween the transition wall 117 and the diameter of the enlarged bodycavity 106. An annular piston face 115, thereby, forms a transitioncavity 119 with the transition wall 117.

The outer face of piston 110 bears against a rod 116 which passesthrough an aperture in an end closure 118 that is threadedly receivedwithin the body 104. A U-bracket 120 is fixedly held against the end ofbody 104 by the end closure 118, which passes through a hole in theU-bracket. A gasket 122 is positioned between the end face of the body104 and the U-bracket 120 and a seal 124 slidably surrounds the rod 116to prevent leakage of hydraulic fluid between the rod 116 and the endclosure 118.

The control line 90, shown in FIGS. 3 and 4, which senses the systempressure imposed by the variable load 4, transmits hydraulic fluid tothe reduced body cavity 108 through a standard threaded connector whichis threadedly received by body 104. Hydraulic fluid conveyed throughcontrol line 90 exerts pressure against a reduced piston surface area113 to move the piston 110 to the right from its position shown in FIG.5. The control line 88 described in FIGS. 3 and 4 enters the body 104through a side port 125. When the discharge from pump 46 is directed tothe system, as illustrated in FIG. 3, the discharge pressure from pump46 is conveyed through control line 88 to the throttle control device102 and exerts pressure against the annular piston face 115. This alsoexerts a force which pushes the piston 110 to the right from itsposition shown in FIG. 5.

The pressure exerted on the annular piston face 115 is proportional tothe volume of fluid discharged to the system by pumps 46 and 48 (FIGS. 3and 4) since pressure is exerted against piston area 115 only when pump46 is discharging hydraulic fluid to the system. The pressure exerted onpiston surface 113 through control line 90 is, on the other hand,proportional to the system pressure and the pressure demands of thevariable load. Thus, the movement of piston 110 reflects both the volumeof hydraulic fluid discharge to the load system by pumps 46 and 48 and,also, the pressure demands imposed by the variable load. The inputtorque required for operation of pumps 46 and 48 is determined by boththe pressure demands of the variable load 4, and also the volume offluid discharged to the system by the pumps. Thus, the movement of thepiston 110 is controlled by the same variables which determine the inputtorque required for operation of pumps 46 and 48.

The outer end of the rod 116 is connected through a pivot support 126 toa clevis 128. The clevis 128 contains an aperture 130 which receives acontrol lever 132. The control lever 132 is held within aperture 130 bymeans of a set screw 134 that is threadedly received by the clevis 128and bears against control lever 132.

The lower end of the control lever 132 engages a pivot opening 142.Thus, as the control rod 116 is moved outwardly through movement ofpiston 110, the control lever 132 is pivoted with respect to the pivotopening 142 which acts as a fulcrum. During the pivoting of controllever 132, the clevis 128 undergoes pivotal movement with respect to rod116 about the pivot support 126. After rotation of the control lever 132through movement of the rod 116, the control lever may, for example,occupy the position illustrated as 132a.

A throttle cable 114 is connected to an opening 145 in the control lever132 adjacent its upper end. The other end of the throttle cable 144 isattached to a throttle lever as depicted at 24 in FIG. 1. As the rod 116is extended and the control lever 132 is pivoted, the throttle lever, isthereby moved by the throttle cable 144 to vary the amount of fuel beingfed to the engine.

A spring 121 is positioned within the enlarged body cavity 106 andsurrounds the rod 116. With the piston 110 in its retracted position,there is a gap 127 between the end of the spring 121 and the outersurface of the piston 110. Thus, as hydraulic fluid is initiallyreceived by the throttle control device 102 through control lines 88 and90, there is a rapid movement of piston 110 and rod 116 to the rightfrom their positions shown in FIG. 5. When the movement of piston 110brings it into engagement with spring 121, the continued movement ofpiston 110 and rod 116 is slowed down by the resistive force of thespring. The function of the throttle control device 102 is to controlthe fuel supplied to the engine in such a manner that the output torquefrom the engine approximates the input torque required for operation ofpumps 46 and 48. Thus, the spring 121 is designed to have a spring ratewhich provides a movement of rod 116 in response to the pressuresexerted on the piston 110 to produce an engine output which approximatesthe required input torque to pumps 46 and 48.

The movement of the engine throttle lever in response to movement of rod116 may also be controlled by the position of the control lever 132. Asthe control lever 132 is pivoted, the movement experienced by thethrottle cable 144 is a function of the moment arm between the opening145 and the pivot opening 142. This distance can be lengthened orshortened by loosening the set screw 134 and moving the control rod 132upwardly or downwardly within aperture 130. In addition, the movement ofthe engine throttle may be varied by providing a plurality of openings148, 150, 152, 154, etc. in the control lever 132. By moving theattachment of the throttle cable 144 from opening 145 to opening 148,the degree of movement of cable 144 will be reduced when the lever 132is rotated. Also, if the control lever 132 is moved downwardly byloosening the set screw 130, the throttle cable 144 may be attached toan opening such as 152 or 154 which is positioned very close to pivotopening 142. This provides a very short movement of cable 144 inresponse to pivoting of control lever 132.

In the operation of the throttle control device 102, the output torqueof the engine is varied in response to the power demands of the variableload. However, at the same time, the speed of the engine is maintainednear its idling speed. An adjustable stop 136 limits the maximummovement of the rod 116 and the maximum rotation of the control lever132. The adjustable stop 136 is composed of a screw 138 retained withinan aperture in U-bracket 120 by nuts 140 which threadedly engage thescrew 138 and bear against opposite sides of the U-bracket. By adjustingthe position of screw 138, the maximum movement of rod 116 and themaximum rotation of control lever 132 may be varied to control themaximum engine speed in providing power for the auxiliary load.

To ensure a low hysteresis loss and a quick movement of piston 110 androd 116, the piston 110 has a relatively loose fitting engagement withthe diameters of reduced body cavity 108 and enlarged body cavity 106.This permits hydraulic fluid to pass between the exterior surfaces ofpiston 110 and the diameters of cavities 106 and 108. A return line 146conveys hydraulic fluid from the enlarged body cavity 106 to areservoir, as shown at 14 in FIG. 1. Thus, there is a slow but constantflow of hydraulic fluid through the throttle control device 102 duringits operation.

The use of the present apparatus and method in operating a packingmechanism for a refuse truck is illustrated in FIG. 6. A refusecollection vehicle 156 including a cab 158 and a refuse containing body160 mounted on a frame 162, has a tailgate 164 positioned rearwardly ofthe body 160. The tailgate 164 may be pivotally mounted at its top tothe body 160 such that it can be rotated upwardly for ejection of refusefrom the body.

As shown in phantom line drawing, the tailgate 164 contains a hopper 166and a packing mechanism 168 mounted within the tailgate 164. The packingmechanism may include one or more packing panels which are actuatedhydraulically, e.g. through use of hydraulic cylinders, to move refusefrom the hopper 166 through an opening positioned in the regionidentified by numeral 170 between the hopper 164 and storage body 160.The particular form of the packing mechanism is not critical to thepresent invention and any hydraulically operated mechanism may be used.

The packing mechanism 168 is operated by a pump 6 driven by the vehicleengine 2 at a speed near the engine idling speed. The pump 6 receiveshydraulic fluid from a reservoir 14 through line 16 and supplies fluidto the packing mechanism 168 through line 10. Hydraulic fluid isreturned to the reservoir 14 from the packing mechanism 168 through line12. In identifying the engine, pump, reservoir, etc., the same referencenumerals are used as in FIG. 1. A throttle control and a means forvarying the output volume and pressure of the pump 6 may be included inthe system shown in FIG. 6 for the reasons described previously withregard to FIG. 1. Also, a clutch 26 and means to operate the clutch(shown in FIG. 1) may be utilized in the system of FIG. 6 to disengagethe drive between engine 2 and pump 6 when the engine speed reaches apredetermined level. This prevents the pump 6 and packing mechanism 168from being overdriven by the engine 2. Additionally, a variabledisplacement pump (FIG. 2) or a plurality of fixed displacement pumps(FIGS. 3 and 4) may be used as the pump 6 in FIG. 6. This permitsvarying the volume and pressure of hydraulic fluid supplied to thepacking mechanism 168 in response to the load demands of the mechanismto maintain the input torque to the pump 6 below a predetermined level.Preferably, the fuel supplied to the engine 2 is also varied in responseto the volume and pressure of fluid supplied to the packing mechanism168 through the use of a throttle control device such as that shown inFIG. 5. This permits varying the output torque of the engine 2 in amanner which is correlated with variations in the input torque requiredby the pump 6. The engine output is, thus, more efficiently used by thepump in driving the packing mechanism 168.

As illustrated by the foregoing description, the invention provides anapparatus which is quite versatile in providing power for operation of avariable volume and a variable pressure auxiliary load. By driving theauxiliary load with a relatively large engine operating near its idlingspeed, the operation is carried out at low noise levels and with reducedengine wear. Moreover, the torque output of the engine is moreeffectively utilized by the load to provide a more efficient use of theengine output.

Throughout the foregoing description, the engine has been described asperforming a secondary work function in providing power for an auxiliaryload. If desired, however, the overall system of the present inventioncould be used in providing power to a primary load using a sufficientlyoversized engine to power the load at a relatively low engine speed nearits idling speed. Although this would increase the initial investment inrequiring a larger engine, this investment cost would be offset by areduction in the resulting noise levels which might justify theincreased cost depending on the particular use application.

Also, as described previously, the auxiliary load has been illustratedas a variable volume and variable pressure load since this is the areawhere the invention has the greatest application. If desired, theapparatus and method of the present invention may be used in operating avariable volume-constant pressure load, a variable pressure-constantvolume load or a constant volume-constant pressure load. By using theprinciples of the present invention, any of these various types of loadsmay be operated at low noise levels which would be highly desirable inreducing the effect of noise pollution on the ecology.

The throttle control device, 102, as described previously, functions asa governor in limiting engine speed as well as functioning to vary thefuel supplied to the engine in response to the power demands of the loadand the input torque requirements of the pump or pumps. If desired,depending on the size of the engine and the demands of the auxiliaryload, the engine may be controlled simply by a governor to limit itsspeed in operation of the load. If, for example, the engine employed isa diesel, the engine speed may be also controlled by an underspeedthrottle control to maintain a given minimum engine speed and to notpermit the engine to operate at a slower speed while providing power tothe auxiliary load.

As described previously, the engine may provide power directly to a pumpor pumps in driving an auxiliary load. Also, however, the pump may bedriven by the engine through an intermediate power means such as anelectric motor. Thus, for example, the engine may drive an auxiliaryalternator to supply power to an electric motor used to drive the pumpor pumps.

A speed control means, such as an electric clutch, may be used toprevent the engine from overdriving the pump or the load, as describedpreviously. Also, however, a speed override may be used to preventincrease in engine speed above a predetermined level by the vehicleoperator when the engine is drivingly engaged with the pump and theload.

I claim:
 1. A noise reduction apparatus for operating a variable volume and variable pressure auxiliary load, said apparatus comprising:pump means having a capacity which is sufficiently large to supply said load at a relatively low pump speed; said pump means including a plurality of fixed displacement pumps supplying hydraulic fluid to the variable load; means to vary the number of pumps supplying fluid to the load in response to the demands of the load; engine means operably connected to said pump means for supplying power to said pump means in performing a secondary work function at a speed near the idling speed of said engine means; throttle control means governing the flow of fuel to the engine means to maintain its horsepower output at a level sufficient to operate the pump means while maintaining the speed of said engine means at a speed near its idling speed; and means to maintain the flow rate from the pump means at a sufficiently low level to not exceed the capacity of the pump means or the auxiliary load when the engine speed is increased to a predetermined level in excess of its idling speed; whereby the engine means operates in the low noise level region of speeds near its idling speed or less when supplying power for the pump means in operating the variable volume and variable pressure load, and the pump means and auxiliary load are protected from use in excess of their capacity when the engine means is operating at increased speeds.
 2. A noise reduction apparatus as defined in claim 1 wherein the number of fixed displacement pumps supplying fluid to the variable load is decreased when the pressure demands of the load are increased to maintain the torque required to drive the pumps below a predetermined level.
 3. A noise reduction apparatus for operating a variable volume and variable pressure auxiliary hydraulic load comprising:a variable pressure and variable volume pump means; engine means operably connected to the pump means for supplying power to the pump means in performing a secondary work function at speeds near the idling speed of the engine means; a fluid reservoir in flow communication with the pump means and the auxiliary load to provide a variable volume of hydraulic fluid for operation of the variable load; means to vary the output pressure and volume of hydraulic fluid from the pump means in response to the demands of the variable load; said pump means including a plurality of fixed displacement pumps with the number of pumps supplying fluid to the variable load being varied in response to the demands of the variable load; throttle control means governing the flow of fuel to the engine means to maintain a torque output of the engine means at a level sufficient to operate the pump means under various loading conditions imposed by the variable load; said throttle control means being actuated in response to the volume and pressure of fluid discharged by the pump means to the variable load, and means to maintain the flow rate of fluid to the variable load at or below a predetermined level.
 4. In combination, a throttle control device for varying the quantity of fuel fed to an engine and a plurality of fixed displacement pumps driven by the engine and providing hydraulic fluid to drive a variable load comprising:means to vary the number of pumps discharging hydraulic fluid to the load in response to the demands of the load; first sensing means to transmit pressure to the throttle control device from the pumps with the transmitted pressure being proportional to the number of pumps discharging fluid to the variable load; second sensing means to transmit pressure to the throttle control device with the transmitted pressure being proportional to the pressure of the hydraulic fluid fed to the load by the pumps; first pressure receiving means in the throttle control device for receiving pressure from the first sensing means; second pressure receiving means in the throttle control device for receiving pressure from the second sensing means, and means in the throttle control device actuatable by the first and second pressure receiving means to transmit movement to the engine throttle with the degree of movement being dependent on both the pressure and volume of fluid discharged by the pumps, whereby the torque output of the engine is varied in response to the torque input required to drive the pumps.
 5. The combination of claim 4 wherein the throttle control device includesa movable piston having differential pressure receiving areas, with one of said areas receiving the pressure from the first sensing means and another of said areas receiving the pressure from the second sensing means, and said piston being operably connected to the engine throttle control to transmit movement to the throttle control in response to the volume and pressure of fluid discharged to the load by the pumps.
 6. The throttle control device of claim 5 including spring means resiliently biasing said piston to a retracted position and imposing a resistive force to movement of said piston.
 7. The throttle control device of claim 6 including a gap between the spring means and the piston when the piston is in a retracted position, wherebythe initial movement of the piston in response to pressure received from the pump is relatively rapid to provide a quick initial response of the throttle control device when the pumps begin their operation.
 8. The combination of claim 4 includingstop means in the throttle control device to limit the degree of movement imparted to the engine throttle. 